Integrated geochemical evaluation of hydrocarbon source potential in late quaternary sediments of the Nkhata basin, Malawi

Abstract The Nkhata basin located in the central part of the Malawi rift consists of Late Quaternary (Chibanian to present; <750 ka) sediments and are the youngest sediments within the great East African Rift System. Rock-Eval pyrolysis and Total Organic Carbon (TOC) analysis of 163 samples from cores GLAD7_MAL05_1B (56–390 m) and GLAD7_MAL05_1C (0–78 m), drilled in the western-central basin, integrated with X-ray Fluorescence (XRF) data are used to assess the source potential of these organic matter-rich sediments within Lake Malawi. Results reveal intervals of good to excellent organic matter-rich silty clay and carbonate mud (TOC > 6.02 wt% and S2 > 25.55 mg HC/g rock; 1 C: TOC up to 6.16 wt%, S2 up to 56.9 mg HC/g rock). The sediments were dominated by oil prone Type II and mixed Type II/II kerogens. Despite wide range TOC values (0.25–7.22 wt%) sandy silty clay facies show poor to good organic quantity and is dominated by Type III/IV kerogens. The overall thermal maturity index suggests immature to early oil window (Tmax: 327–444 °C; PI: 0.01–0.64) sediments. Redox proxies (V/Cr, V/(V + Ni), S/Fe) show deposition occurred under predominantly oxic-dysoxic bottom waters, with two discrete anoxic/euxinic events (1B: 186 m, 288–298 m). These events correlate with peak TOC values (6.02 wt% at 274.3 m), signifying that episodic euxinia significantly enhanced organic matter preservation by suppressing aerobic degradation. The Nkhata Basin exhibits compelling source rock characteristics comparable to other productive basins within the East African rift system but requires deeper burial to achieve generative maturity.